Interstellar Messages Suppose that we did pick up a signal, or perhaps began sending one ourselves. What form should it take? Anticryptography Much effort is spent these days developing cryptographic methods to make it difficult for anyone without the key to decode the message. Here we want the exact opposite, anticryptography as it has been called, where the objective is to make the message decipherable by any intelligent beings about whom we know nothing. We want a message that effectively decodes itself without any prior knowledge about its form or contents. Here is one simple example: Try it! Suppose that you receive a radio signal at a frequency of 1400 Mhz which is a repeating sequence of dots and dashes - it MUST repeat otherwise you could NEVER decode it! ALL you can do initially is to count the sequence of dots and dashes and find that it repeats after 667 dots and dashes. If such a message is received it would be looked at by scientists of every discipline and within moments someone would spot that the number 667 has only two divisors, 23 and 29 - both prime numbers! This suggests that the message might represent a two dimensional array either 23 lines of 29 boxes or 29 rows of 23 boxes. Each box can have only one of two states corresponding to either a dot and a dash, so let's make the dots white and the dashes black. The first way round just gives a pretty meaningless jumble but the second looks more interesting!
Just to help here is a version where the different parts of the message have been colour coded in order to make it more obvious. (Of course, you couldn't do this until the scientists had worked out what it all meant.) What do the different colours represent? Try it yourself before you read the answer!